6th International Conference on Gas Hydrates


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   DEVELOPMENT OF A MONITORING SYSTEM FOR THE JOGMEC/NRCAN/AURORA MALLIK GAS HYDRATE PRODUCTION TEST PROGRAM   Kasumi Fujii* and Masato Yasuda Japan Oil, Gas and Metals National Corporation 1-2-2 Hamada Mihama-ku, Chiba JAPAN  Brian Cho, Toru Ikegami, Hitoshi Sugiyama and Yutaka Imasato Schlumberger K.K., JAPAN  Scott R. Dallimore and J. Frederick Wright Geological Survey of Canada, CANADA   ABSTRACT Design and construction of long term gas hydrate production facilities will require assessment of the in situ formation response to production at a field scale. Key parameters such as temperature and pressure are critical for the determination of phase conditions, others such as formation resistivity, formation acoustic properties and fluid mobility support the inference of gas hydrate saturation, permeability and porosity. An ability to continuously monitor the response of these parameters during the course of a production test would facilitate tracking of the dissociation front and yield valuable information for engineering design and verification of numerical reservoir simulators. Such a monitoring system has been designed, developed and introduced as a part of the Japan Oil, Gas and Metals National Corporation and Natural Resources Canada gas hydrate production testing program carried out in the winter of 2007 in the Mackenzie Delta, Canada.  While the deployment of some sensors and the acquisition of some data sets were limited due to operational problems encountered during the field program, considerable experience has been gained during all phases of the research program.  In particular, the acquisition and interpretation of downhole temperature profiles and changes in formation electrical potentials during testing provide insight into the production response of the reservoir and may assist in the understanding of operational conditions and related decision-making processes.  Keywords: gas hydrate, dissociation, monitoring, temperature   * Corresponding author: Phone: +81 43 276 4526 E-mail: fujii-kasumi@jogmec.go.jp, currently in Schlumberger K.K. INTRODUCTION The 2006-08 JOGMEC/NRCan/Aurora Mallik gas hydrate production research program is being conducted with a central goal to measure and monitor the production response of a terrestrial gas hydrate deposit to pressure draw down. The Japan Oil, Gas and Metals National Corporation (JOGMEC) and Natural Resources Canada (NRCan) are funding the program and leading the research and development studies. Aurora College/Aurora Research Institute is acting as the operator for the field program. In support of the acquisition of critical reservoir parameters and to facilitate tracking of the Proceedings of the 6th International Conference on Gas Hydrates (ICGH 2008), Vancouver, British Columbia, CANADA, July 6-10, 2008. dissociation front, we have conceptualized, designed, and developed a state-of-the-art downhole monitoring system for gas hydrate applications. The system was designed to be installed mainly on the outside of the well casing of a production or observation well, enabling continuous monitoring during production testing regardless of wellsite operations. During the winter of 2006-07, a number of sensor cables were deployed on the outside of the production well casing. Operational difficulties and severe arctic conditions prevented the successful installation of some of the cable strings, resulting in the failure or partial failure of some sensors. A specially-designed oriented perforation system successfully perforated the well casing while avoiding any damage to the monitoring cables. Drilling of an observation well dedicated to monitoring was also planned, but this activity was abandoned due to schedule constraints. Complimentary papers also published in this volume describe well-site operations [1], well logging and interpretation [2], numerical modeling scenarios [3], and geological context [4].  MONITORING CONCEPT The primary justification for the development of a downhole monitoring system was the requirement for real-time acquisition of key reservoir parameters (such as porosity, permeability, temperature, pressure, and hydrate saturation) from downhole measurements throughout the production test period. These parameters were considered as critical to understanding the in situ properties and behavior of gas hydrate and its dissociation response to production stimulation. A second aim was to monitor the progression of the dissociation front with a reasonable resolution in both the vertical and horizontal directions. Based on these requirements, a variety of measurement methodologies and available technologies were investigated. Some of these technologies were considered immature but promising candidates for further development. The Mallik project provided an opportunity for the validation of these technologies, in terms of their operability and performance in a gas hydrate application.  CANDIDATE MONITORING ELEMENTS As possible candidate monitoring elements, the following property measurements were examined through laboratory experiments and numerical studies [5][6][7][8]. Pressure/Temperature These fundamental parameters are sensitive to the phase condition of gas hydrate. A comparison of the measured in situ temperature and pressure condition to a known gas hydrate phase equilibrium curve supports estimation of the phase state and thermodynamic stability of gas hydrate.  Electrical Resistivity The electrical resistivity of gas hydrate-bearing and non-hydrate-bearing sediments is expected differ significantly [9][10], with generally higher resistivity where hydrate is present and lower resistivity following gas hydrate dissociation (possibly as a function of dissolved ion concentrations). Conceptually, by measuring the resistivity profiles at the different depths of investigation using electrode arrays, the progression of the dissociation front can be monitored as a resistivity image.  Fluid mobility Although at higher saturation levels gas hydrate- bearing sediments contain little mobile fluid, upon hydrate dissociation gas and water are released. Therefore, fluid mobility will be largely affected by the amount of gas hydrate present before, during, and after dissociation. The measurement of changes in electrical potential created by pressure perturbation and corresponding movement of charged fluids within sediment pores and/or fractures at the fluid-solid interface (streaming potential) should facilitate estimation of the apparent fluid permeability [11].  Thermal Conductivity The thermal conductivity (TC) of hydrate-bearing and non-hydrate-bearing sediments may not differ greatly [12][13], although obtaining in situ thermal properties will contribute to the development of efficient production methods [14]. The TC of cores is often measured upon recovery to the surface, and laboratory measurements of TC of synthetic gas hydrate in both natural and artificial; porous media has become routine. Henninges et al. [12] and Wright et al. [13] employed DTS-derived temperature profiles to estimate the TC of sediments within the Mallik reservoir during the 2002 Mallik gas hydrate production research program, but no direct in situ TC measurement of a gas hydrate-bearing formation has yet been accomplished downhole. The acquisition of in situ TC measurements is considered useful for comparison and evaluation against core data, for which the preservation and maintenance of in situ physical and thermal properties are usually very difficult.  Cross-well Acoustic Tomography Acoustic parameters such as formation velocity and attenuation are observed to have different behaviors in hydrate-bearing vs. non-hydrate- bearing sediments. Generally higher acoustic velocities and increased attenuation are observed in the presence of hydrate, as compared to measurements obtained following gas hydrate dissociation[15][16]. Differences in compressional velocity before and after dissociation may make it possible to monitor the progression of the dissociation front using first-break traveltime tomography.  FIELD INSTALLATION A limited suite of monitoring sensor cables was successfully deployed in the Mallik 2L-38 production well during the winter of 2006-07. A set of optical fiber cables was installed as the downhole component of a Distributed Temperature Sensing (DTS) system, enabling continuous and relatively high resolution downhole temperature measurement. In addition, an array of electrodes for measurement of electrical resistivity and streaming potential was deployed, and the surface of the well casing was coated by an electrical insulation jacket in sections where electrodes were deployed. All cables were strapped to the casing at the surface, installed along the outside of the well casing, after which the annulus between the casing and the formation was filled with the cement. The surface extension of each cable was run through a conduit connecting to individual data acquisition systems located in a nearby monitoring house. Although all cables and their mounting hardware (clamps and centralizers) were designed to maximize protection of the cables and minimize the risk of inadvertent damage, the DTS cable was damaged approximately 34 m above the top of the planned perforation interval. Although it was still possible to collect temperature data above that depth, the preferred double-ended (loop) measurement technique had to be abandoned. Instead, a single-ended measurement technique was employed, still enabling continuous temperature measurement with reduced accuracy. A 6-sensor electrode-array cable dedicated to measurement of streaming potential was deployed in the lower hydrate zone targeted for first-winter production testing in 2006-07. Two electrodes were set within the perforated interval, and two electrodes were installed above the perforated interval (but still in hydrate zone) as planned. The two remaining electrodes were abandoned due to an irresolvable contact resistance issue. A second electrode-array cable dedicated to resistivity measurement was set within an upper hydrate zone scheduled for production testing in the following winter (2008), and thus could not be utilized during the 2006-07 production test. Figure 1 shows the cable mounting configuration and hardware prior to deployment into the well (left), and presents an example of the perforation pattern produced by the oriented perforation system utilized (right).   Figure 1 Cable mount and clamp on casing with an electrical insulation jacket (left) and oriented perforation of casing (right)  RESULTS During the winter of 2006-07, datasets for all working sensor strings were acquired to confirm sensor functions and for quality control purposes. For the DTS temperature measurement system, data averaged across 10 minutes intervals yielded a temperature resolution of approximately 0.1 ºC (standard deviation), with an estimated accuracy of approximately 1.5 ºC after surface calibration and with reference to downhole temperature logs.  DTS and cementing operations Figure 2 shows the temperature variation in depth and time acquired during the cementing operations. The temperature increase due to the release of hydration heat during curing of the cement can be easily observed. Immediately upon injection of the cement down the casing, the overall well-bore temperature increased slightly. After the cement exited the bottom of the casing and began to flow up the wellbore (outside of casing), an additional and somewhat stronger increase in wellbore temperature was observed, progressing from the bottom up. Once the cement was settled into position between the casing and formation, further increases in wellbore temperatures were generally proportional to the well-bore size as shown in Figure 3, indicating a simple heat conduction process. After an initial modest warming, well temperatures at shallower depths began to trend towards the background formation temperatures. In addition to providing information on the location of cement within the casing and annulus, such observations of temperature evolution along the wellbore also support estimation of the amount of heat generated during the cementation process, and evaluations of the thermal impact of the cementing process on gas hydrate within the formation adjacent to the wellbore.   Figure 2 DTS temperature profiles acquired during the cementation process   Figure 3 DTS temperature increase (right axis) by the cementing process with relative to the well- bore diameter (left axis)  DTS and production testing Figure 4 shows the evolution of well temperatures vs. depth for a period of nine days following cementing. The production testing period is bracketed by the dashed red lines. An observed general cooling of the lower portion of the well throughout the production period is assumed to be related to fluid level changes accompanying pressure-drawdown (bringing cooler fluids down from shallower depths). A strong temperature recovery follows immediately after termination of the production test, warming considerably above formation temperatures for that depth. Kurihara [3] proposes that this anomalous warming of bottomhole temperatures may be due to a backflow of warmer fluids from the water injection zone (below 1224 m).   Figure 4 Overall temperature profiles after cementing  DTS and well-kill operations The sharp spike in near-surface temperatures approximately 24 hrs after the end of testing is due to the reverse circulation of warm fluid in the upper section of the well during well-kill operations. Two additional temperature perturbations apparent in the latter portion of the record are consistent with the normal circulation operations from the surface to the well bottom.  Although damage to the sensor cable prevented the acquisition of temperature data in the production zone, the information presented in Figures 2-4 demonstrate that DTS temperature data have considerable utility in support of well-operations and related matters.    Streaming potential Measurements of streaming potential were made at four electrode positions in the area of the production zone. As shown in Figure 5, changes in electrical potential were observed during the production test at two electrodes deployed within the perforated interval, while no significant change was observed at two electrodes located outside the perforated interval. We interpret the data to indicate the movement of produced fluids released by dissociation of gas hydrate in the vicinity of the perforations. Beyond the perforated interval, little or no gas hydrate dissociates, and no significant pressure field exists to draw fluid towards the well bore. Consequently, the low fluid content of the formation and the lack of motive force to transport fluid results in relatively stable electrical potentials for the electrodes located outside of the perforated interval. Given a suitably dense array of sensors, this technique affords a promising potential for qualitative indication of fluid movement within different operations of a gas hydrate reservoir during production testing.    Figure 5 Relative changes in electrical potentials during the production test period. All electrodes are located within gas hydrate zone. Only electrodes located within the perforation interval show significant changes in streaming potential.  CONCLUSION This paper has reviewed a limited suite of sensor data employed in the Mallik 2006-07 gas hydrate production test. Time-series DTS data show a practical utility for this technique in gas hydrate applications, especially with respect to the interpretation of reservoir and well-bore responses to gas hydrate production, and as a useful information basis for operations management and decision-making. Furthermore, data from four operational sensors suggest a promising potential for further development of electrical resistivity techniques for the measurement of streaming potentials and the assessment of fluid dynamics related to gas hydrate production.  ACKNOWLEDGEMENT This study has been supported by Research Consortium for Methane Hydrate Resources in Japan (MH21). The authors wish to thank Japan Oil, Gas and Metals National Corporation (JOGMEC), Natural Resources Canada (NRCan) and MH21 for their permission to publish this paper.  REFERENCES [1] Numasawa M., Dallimore S.R., Yamamoto K., Yasuda M., Imasato Y, Mizuta T., Kurihara M., Masuda Y., Fujii T., Fujii K., Wright J. F., Nixon F. M., Cho B., Ikegami T. and Sugiyama H., Objectives and Operation Overview of the JOGMEC/NRCan/Aurora Mallik Gas Hydrate Production Test, this volume  [2] Fujii T., Takayama T., Dallimore S.R., Nakamizu M., Mwenifumbo J., Kurihara M., Yamamoto K., Wright J.F.,  Al-Jubori A., Tribus M. and Evans R.B. Wire-line Logging Analysis of the JOGMEC/NRCan/Aurora Mallik Gas Hydrate Production Test, this volume  [3] Kurihara M., Masuda Y., Funatsu K., Ouchi H., Yasuda M., Yamamoto K., Numasawa M., Fujii T. and Narita H. Analysis of the JOGMEC/NRCan/Aurora Mallik Gas Hydrate Production Test through Numerical Simulation, this volume  [4] Dallimore S.R., Wright J.F., Nixon, F.M., Kurihara M., Yamamoto K., Fujii T., Fujii K., Numasawa M., Yasuda M. and Imasato Y. Geologic and porous media factors affecting the 2007 production response characteristics of the JOGMEC/NRCan/Aurora Mallik gas hydrate production research well, this volume  [5] Morikami Y., Ikegami T., Chen M.Y., Fujii K., and Yasuda M. Electrical resistivity array measurement system development for gas hydrate dissociation monitoring, this volume  [6] Primiero P., Dreuillault V., Sugiyama H., Ikegami T., Fujii K., Fukuhara M., Chang C. and Yasuda M. Acoustic monitoring of methane hydrate production: System development, deployment and modeling/measurement evaluation, this volume  [7] Ikegami T., Morikami Y., Fujii K., Suzuki K., Imasato Y., Chen M.Y. and Yasuda M. Streaming potential measurement for hydrate dissociation monitoring, this volume  [8] Sakiyama N., Morikami Y., Ikegami T., Shako V., Fukuhara M., Fujii K. and Yasuda M. Numerical study results on active downhole thermal property measurement system for hydrate characterization, this volume  [9] Anderson B.I., Collett T.S., Lewis R.E. and Dubourg I. Using openhole and cased hole resistivity logs to monitor gas hydrate dissociation during a thermal test in the Mallik 5L-38 research well, Mackenzie Delta, Canada. Society of Petrophysicists and Well Log Analysis 46th Annual Logging Symposium, 2005  [10] Riedel M., Kulenkampff J., Spangenberg E., Dallimore S.R. Geophysical properties of sediment core samples obtained from the JAPEX/JNOC/GSC et al. Mallik 5L-38 gas hydrate production research well, in Dallimore, S.R., and T.S. Collett, eds., Scientific Results from the Mallik 2002 Gas Hydrate Production Research Well Program, Mackenzie Delta, Northwest Territories, Canada: Geological Survey of Canada, Bulletin 585, 2005.  [11] Chen M.Y., Raghuraman B., Bryant I. and Supp M. Streaming Potential Applications in Oil Fields. In: Proceedings - SPE Annual Technical Conference and Exhibition 2, 2006, p997  [12] Henninges, J., Schrötter, J., Erbas, K., and Huenges, E. Temperature field of the Mallik gas hydrate occurrence – implications on phase changes and thermal properties, in Dallimore, S.R., and T.S. Collett, eds., Scientific Results from the Mallik 2002 Gas Hydrate Production Research Well Program, Mackenzie Delta, Northwest Territories, Canada: Geological Survey of Canada, Bulletin 585,  2005.  [13] Wright, J.F., Nixon, F.M., Dallimore, S.R., Henninges, J., and Côté, M.M. Thermal conductivity of sediments within the gas-hydrate- bearing interval at the JAPEX/JNOC/GSC et al. Mallik 5L-38 gas hydrate production research well, in Dallimore, S.R., and T.S. Collett, eds., Scientific Results from the Mallik 2002 Gas Hydrate Production Research Well Program, Mackenzie Delta, Northwest Territories, Canada: Geological Survey of Canada, Bulletin 585, 2005.  [14] Morikami Y., Fujii K., Fukuhara M. and Yasuda M. In-Situ Thermal Property Measurement System Development. The 12th Formation Evaluation Symposium of Japan, October 4-5, 2006   [15] Guerin G., Goldber D. and Collett T.S. Sonic attenuation in the JAPEX/JNOC/GSC et al. Mallik 5L-38 gas hydrate production research well, in Dallimore, S.R., and T.S. Collett, eds., Scientific Results from the Mallik 2002 Gas Hydrate Production Research Well Program, Mackenzie Delta, Northwest Territories, Canada: Geological Survey of Canada, Bulletin 585, 2005.  [16] Kleinberg R.L., Flaum C. and Collett T.S. Magnetic resonance log of JAPEX/JNOC/GSC et al. Mallik 5L-38 gas hydrate production research well: gas hydrate saturation, growth habit, and relative permeability,  in Dallimore, S.R., and T.S. Collett, eds., Scientific Results from the Mallik 2002 Gas Hydrate Production Research Well Program, Mackenzie Delta, Northwest Territories, Canada: Geological Survey of Canada, Bulletin 585, 2005.


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